The present invention relates to a method of and an arrangement for optimizing the operation of a distillation column provided with a side heating device, for reconditioning of the extract which is received during the extraction of hydrocarbon-containing starting materials with N-substituted morpholines whose substituents have no more than seven C atoms as selective solvents.
The extraction of hydrocarbon containing starting products with the above-mentioned N-substituted morpholines especially with N-formyl morpholines as selective solvents has been known for a long time and is used nowadays on large scale, first of all for recovery of aromates of high purity. The method is also suitable for recovery of other classes of materials, for example olefin and diolefin, whereas both the extracted distillation as well as liquid-liquid extraction can be utilized. The hydrocarbon to be recovered from the respective starting products concentrates together with the main quantity of the solvent in the extract and must be separated from the solvent in the distillation column located after the extraction stage. The hydrocarbon to be recovered is distilled through the top from the distillation column, while the solvent precipitates as sump product of the column and can be supplied from there for a further utilization. The distillation column can be provided for its heating in addition to the conventional sump circulating heating device, also with a side heating device which first of all must evaporate the return flow from the distillation column.
During operation of such distillation columns especially in connection with the utilization of N-formyl morpholine as selected solvent, it has been determined that the solvent is concentrated on the plate of the distillation column, which lies above the outlet of the heating device and simultaneously is a withdrawing plate for the side heating device. Thereby the boiling temperature on this plate is increased and therefore the heat output of the plate is continuously worsened. By an increase of the return flow the heat discharge of the side heating device can be increased. This, however brings no advantage, since the sump circulating heating device of the distillation column must supply the same quantity of heat and thereby its total thermal balance is not improved.